Tile drainage causes flashy streamflow response in Ohio watersheds

Samuel Miller
Steve W. Lyon
Environment and Natural Resources

Artificial subsurface (tile) drainage is used to increase trafficability and crop yield in much of the Midwest due to soils with naturally poor drainage. Tile drainage has been researched extensively at the field scale, but knowledge gaps remain on how tile drainage influences the streamflow response at the watershed scale. The purpose of this study is to analyze the effect of tile drainage on the streamflow response for 59 Ohio watersheds with varying degrees of tile drainage and explore patterns between western Lake Erie algal bloom severity to streamflow response in heavily tile-drained watersheds. Tile drainage percentage for each watershed was estimated from a new 30-m resolution dataset. Daily streamflow was downloaded from 2010-2019 and used to calculated mean annual peak daily runoff, mean annual runoff ratio, the percent of observations in which daily runoff exceeded mean annual runoff (TQmean), and baseflow. Heavily tile-drained watersheds (40 % of area) consistently reported flashier streamflow behavior compared to watersheds with low amounts of tile drainage (15% of area) as indicated by significantly lower baseflow percentages and TQmean. Mean annual baseflow percentage for heavily tile-drained watersheds was 20.9% compared to 40.3% for watersheds with low amounts of tile drainage. These results are in contrast to similar research regionally indicating greater baseflow percentages and less flashy streamflow (higher TQmean) for heavily-tiled watersheds. The total amount of March-July stormflow (i.e. runoff not comprised of baseflow) in heavily tile-drained watersheds and the stormflow runoff ratio during this time was significantly positively correlated to western Lake Erie harmful algal bloom severity during the study period. Given the recent trend in more frequent large rain events and warmer temperatures in the Midwest, increased harmful algal bloom severity will continue to be an ecological and economic problem for the region if management efforts are not addressed at the source. Management efforts that reduce the streamflow response following storm events, such as buffer strips, wetland restoration, or drainage water management, are likely to improve the aquatic health conditions of downstream communities by limiting the transport of nutrients following storm events.